CN112697303B - Distributed optical fiber sensing system and detection method for smart grid - Google Patents
Distributed optical fiber sensing system and detection method for smart grid Download PDFInfo
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Abstract
The invention belongs to a distributed Raman fiber sensing system, and discloses a distributed fiber Raman sensing system and a detection method facing a smart grid and considering both long sensing distance and high spatial resolution, wherein the system comprises a pulse laser, a wavelength division multiplexer, a sensing fiber, a first photoelectric detector, a second photoelectric detector and a data acquisition system, the pulse laser output by the pulse laser is incident to the sensing fiber after passing through the wavelength division multiplexer, Stokes light and anti-Stokes light reflected in a sensor are transmitted to the data acquisition system after passing through the wavelength division multiplexer and detected by the first photoelectric detector and the second photoelectric detector, one part of the sensing fiber is arranged in a thermostatic bath, and the thermostatic bath is used for carrying out thermostatic control on the sensing fiber positioned in the thermostatic bath; the data acquisition system is used for acquiring and demodulating data to obtain distributed temperature field information along the sensing optical fiber. The invention improves the resolution and the measurement precision of the system, and can be applied to the field of intelligent power grid detection.
Description
Technical Field
The invention belongs to a distributed Raman fiber sensing system, and particularly relates to a distributed fiber Raman sensing system and a detection method for a smart grid, wherein the distributed fiber Raman sensing system and the detection method have long sensing distance and high spatial resolution.
Background
High voltage transmission networks throughout the country have become the fate of modern industry and national economy. With the increasing complexity and precision of power supply networks, the problem of safety monitoring of the power networks is more and more urgent. Because many links in the power supply system are easily disturbed by various factors, if hidden dangers and faults existing in the power supply system cannot be found in time, serious safety accidents are easy to happen. However, the current single-point, multi-probe and single-parameter sensor cannot meet the requirement of large-range long-distance detection of the power supply network.
The distributed optical fiber Raman sensing system can continuously measure the distributed temperature characteristic information along the sensing optical fiber. The system demodulates the temperature change along the optical fiber by collecting the back Raman scattering light carrying temperature information generated when the pulse light is transmitted in the optical fiber, and then performs positioning according to the optical time domain reflection technology, thereby realizing distributed continuous measurement of the temperature along the sensing optical fiber. In the distributed optical fiber Raman temperature measurement system, the spatial resolution refers to the minimum length of the temperature measurement system capable of distinguishing the temperature change of the optical fiber. At present, a distributed fiber raman temperature sensing system uses an Optical Time Domain Reflectometry (OTDR) technique for positioning, and the optimal spatial resolution can reach 1 m. However, due to the limitation of the pulse width of the light source, there is a contradiction that the spatial resolution and the sensing distance cannot be compatible in the method.
Because the temperature change caused by the fault in the power grid has the characteristics of small range and large amplitude, the fault position in the power grid can be positioned by distributed temperature measurement, but when the spatial resolution of the distributed Raman sensing system in the prior art is large, the temperature change system in the extremely small range caused by the power grid fault is difficult to accurately measure, and the specific expression is that the measured temperature change amplitude is far lower than the actual temperature of a fault point, and the system is easily missed to report under the condition. Based on this, it is necessary to improve the distributed optical fiber sensor system in the prior art to meet the distributed detection requirement of the smart grid.
Disclosure of Invention
The invention overcomes the defects of the prior art, and solves the technical problems that: the distributed optical fiber Raman sensing system and the detection method for the smart grid with consideration of both long sensing distance and high spatial resolution are provided, so that the problem that the spatial resolution and the sensing distance of the existing distributed optical fiber Raman sensing system cannot be considered at the same time is solved, and the spatial resolution of the system is improved to 1 cm.
In order to solve the technical problems, the invention adopts the technical scheme that: a distributed optical fiber sensing system facing a smart grid comprises a pulse laser, a wavelength division multiplexer, a sensing optical fiber, a first photoelectric detector, a second photoelectric detector and a data acquisition system, wherein pulse laser output by the pulse laser is incident to the sensing optical fiber after passing through the wavelength division multiplexer, Stokes light and anti-Stokes light reflected in a sensor are detected by the first photoelectric detector and the second photoelectric detector after passing through the wavelength division multiplexer, one part of the sensing optical fiber is arranged in a thermostatic bath, and the thermostatic bath is used for carrying out thermostatic control on the sensing optical fiber positioned in the thermostatic bath; the Stokes signals and the anti-Stokes signals detected by the first photoelectric detector and the second photoelectric detector are collected and demodulated by a data collection system to obtain distributed temperature field information along the sensing optical fiber.
The data acquisition system comprises a data acquisition card and a calculation unit.
The distributed optical fiber sensing system facing the smart grid further comprises a first amplifier and a second amplifier, and output signals of the first photoelectric detector and the second photoelectric detector are collected by a data acquisition card after passing through the amplifiers.
The sampling rate of the data acquisition card is 10GS/s, and the bandwidth is 10 GHz.
The wavelength of the pulse laser is 1550nm, the pulse width is 10ns, and the repetition frequency is 6 KHz; the bandwidths of the first photoelectric detector and the second photoelectric detector are 100MHz, and the spectral response range is 900-1700 nm; the sensing optical fiber is a refractive index graded multimode optical fiber.
The temperature demodulation formula is as follows:
wherein T represents the temperature of the nth measuring interval of the sensing optical fiber outside the thermostatic bath, k is Boltzmann constant, Deltav is Raman frequency shift, h is Planckian constant, and T is obtained by demodulationcFor measuring the set temperature, T, of the thermostatic bath during the phasec0For calibrating the set temperature, T, of the thermostatic bath0Sensing the ambient temperature of the fiber for calibration stage, Ial0Indicating the intensity of the backward Raman anti-Stokes scattered light, I, of the respective measurement interval in the thermostatic bath obtained in the calibration phasealnIndicating obtained constants of calibration phaseThe light intensity of the backward Raman anti-Stokes scattered light in the nth measurement interval of the sensing optical fiber outside the warm tank is Iac0Indicating the intensity of the backward Raman anti-Stokes scattered light of each measurement interval in the thermostatic bath obtained during the measurement phase, IacnThe optical intensity of backward Raman anti-Stokes scattered light obtained in the nth measurement interval of the sensing optical fiber outside the constant temperature bath in the measurement stage is represented; i issl0Indicating the intensity of the backward Raman Stokes scattered light of each measurement interval in the thermostatic bath obtained in the calibration phase, IslnIndicating the intensity of the backward Raman Stokes scattered light of the nth measuring interval of the sensing fiber outside the thermostatic bath obtained in the calibration stagesc0Indicating the intensity of the backward Raman Stokes scattered light of each measurement interval in the thermostatic bath obtained in the measurement phase, IscnAnd the light intensity of backward Raman Stokes scattered light obtained in the nth measurement interval of the sensing optical fiber outside the constant temperature bath in the measurement stage is shown, and n is a positive integer greater than zero.
Ialn、Isln、Iacn、IscnThe calculation formulas of (A) and (B) are respectively as follows:
wherein X is equal to the ratio of the pulse width to the length of the sampling interval; I.C. Aan' and Ia(n-1)' Backward Raman anti-Stokes scattering of nth and (n-1) th sampling intervals of the fiber outside the thermostat obtained in the calibration stageIntensity of the emitted light, Ial(n-X)Indicating the intensity of the backward Raman anti-Stokes scattered light of the n-X measurement interval outside the thermostatic bath obtained in the calibration stage, Ia0' represents the light intensity of the anti-stokes light of the last sampling interval in the thermostatic bath obtained in the calibration stage;
Isn' and Is(n-1)' indicating the intensity of the backward Raman Stokes scattered light in the n-th and n-1-th sampling intervals of the fiber outside the thermostat obtained in the calibration stage, respectively, Isl(n-X)Indicating the light intensity of backward Raman Stokes scattered light of the n-X measurement interval outside the constant temperature bath obtained in the calibration stage; i iss0' indicating the intensity of stokes light of one sampling interval in the thermostatic bath obtained in the calibration stage;
Ianand Ia(n-1)Respectively showing the light intensity, I, of backward Raman anti-Stokes light in the n-1 th and n-th sampling intervals of the optical fiber outside the thermostatic bath obtained in the measuring stageac(n-X)Indicating the intensity of backward Raman anti-Stokes light in the n-X measurement interval outside the thermostatic bath obtained in the measurement stage, Ia0A light intensity of anti-stokes light representing one sampling interval in the thermostatic bath obtained in the measurement phase;
Isnand Is(n-1)Respectively showing the light intensity, I, of backward Raman Stokes light of the n-1 th sampling interval and the n-th sampling interval of the optical fiber outside the thermostatic bath obtained in the measuring stagesc(n-X)Indicating the intensity of backward Raman Stokes light in the n-X measurement interval outside the thermostatic bath obtained in the measurement stage, Is0Representing the intensity of the stokes light of the last sampling interval in the thermostatic bath obtained during the measurement phase.
In addition, the invention also provides a distributed optical fiber sensing detection method facing the smart grid, which is realized by adopting the system and comprises the following steps:
s1, calibration stage: setting the temperature of the thermostatic bath to Tc0The ambient temperature of the sensing fiber is set to T0Setting the sampling period of the data acquisition system to be 1/X of the width of a single pulse, and acquiring the Raman anti-Stokes reflected in the sensing optical fiber by using the data acquisition systemThe light intensity of the Stokes light and the backward Raman anti-Stokes light I of each sampling interval of the sensing fiber in the constant temperature tanka0' and intensity of backward Raman Stokes light Is0' and the light intensity I of backward Raman anti-Stokes light obtained in each sampling interval of the sensing fiber outside the thermostatic bathan' and intensity of backward Raman Stokes light Isn’；
S2, measurement stage: setting the temperature of the thermostatic bath to TcSetting the same sampling period, and acquiring the light intensities of all Raman anti-Stokes lights and anti-Stokes lights in the sensing optical fiber by using a data acquisition system, including the light intensity I of the backward Raman anti-Stokes scattered light in each sampling interval of the sensing optical fiber in the thermostatic batha0And the intensity of the backscattered Raman Stokes light Is0And the light intensity I of backward Raman anti-Stokes light obtained in each sampling interval of the sensing optical fiber outside the constant temperature bathanAnd the intensity of backward Raman Stokes light Isn；
And S3, calculating and demodulating the data obtained by measurement in the steps S1 and S2 to obtain the distributed temperature field information along the sensing optical fiber (3).
The value of X is 100.
Compared with the prior art, the invention has the following beneficial effects: the invention provides a distributed optical fiber Raman temperature sensing system with long-distance centimeter-level resolution and a demodulation method, which are characterized in that a Stokes light signal and an anti-Stokes light signal generated by collected Raman scattering are reconstructed and analyzed in a layered manner, so that the limitation of the pulse width of a light source of a traditional distributed optical fiber Raman temperature measuring system on the spatial resolution is broken through, the sensing distance is ensured, the spatial resolution of the system is optimized, the spatial resolution is improved, the temperature measurement is more accurate in small-range temperature change, and on one hand, the missing report is prevented, and the monitoring accuracy is improved; on the other hand, temperature measurement is more accurate, makes things convenient for the fault diagnosis, can be applied to in the smart power grids detects.
Drawings
Fig. 1 is a schematic structural diagram of a distributed optical fiber raman sensing system facing a smart grid according to an embodiment of the present invention;
FIG. 2 is a schematic diagram of the measurement of the present invention;
in the figure: 1-pulse laser, 2-wavelength division multiplexer, 3-sensing optical fiber, 4-first photoelectric detector 1, 5-second photoelectric detector, 6-first amplifier, 7-second amplifier, 8-data acquisition card, 9-computer and 10-thermostatic bath.
Detailed Description
In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below, and it is obvious that the described embodiments are some embodiments of the present invention, but not all embodiments; all other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
As shown in fig. 1, an embodiment of the present invention provides a distributed optical fiber raman sensing system facing a smart grid, including a high power pulse laser 1, a wavelength division multiplexer 2, a sensing optical fiber 3, a first photodetector 4, a second photodetector 5, a first amplifier 6, a second amplifier 7, a data acquisition card 8, a computer 9, and a thermostat 10.
The output end of the pulse laser 1 is connected with a first port a of a wavelength division multiplexer, a second port b of the wavelength division multiplexer 2 is connected with a first port a of a sensing optical fiber 3, a part of the sensing optical fiber 3 with the length of 1m is placed in a constant temperature tank 10 at a position with the distance of 5m between the sensing optical fiber 3 and the second port b of the wavelength division multiplexer 2, the third port c of the wavelength division multiplexer 2 is connected with the input end of the avalanche photodetector 4, the fourth port d of the wavelength division multiplexer 2 is connected with the input end of the avalanche photodetector 5, the output end of the avalanche photodetector 4 is connected with the input end of the amplifier 6, the output end of the avalanche photodetector 5 is connected with the input end of the amplifier 7, the output ends of the amplifier 6 and the amplifier 7 are connected with the input end of the high-speed data acquisition card 8, and the output end of the data acquisition card 8 is connected with the computer 9.
Pulse laser output by the pulse laser 1 is transmitted to a sensing optical fiber 3 after passing through a wavelength division multiplexer 2, Stokes light and anti-Stokes light reflected in the sensor 3 are detected by a first photoelectric detector 4 and a second photoelectric detector 5 after passing through the wavelength division multiplexer 2, a part of the sensing optical fiber 3 is arranged in a constant temperature bath 10, and the constant temperature bath 10 is used for carrying out constant temperature control on the sensing optical fiber 3 positioned in the constant temperature bath 10; the stokes signal and the anti-stokes signal detected by the first photoelectric detector 4 and the second photoelectric detector are amplified by the first amplifier 6 and the second amplifier 7 respectively, data are collected by the data collection card and then sent to the computer, and the computer collects and demodulates the collected data to obtain the distributed temperature field information along the sensing optical fiber 3.
Further, in this embodiment, the wavelength of the pulse laser 1 is 1550nm, the pulse width is 10ns, the repetition frequency is 6KHz, and the output peak power is 5W; the bandwidths of the first photoelectric detector 4 and the second photoelectric detector 5 are 100MHz, and the spectral response ranges are 900-1700 nm. The data acquisition card 8 is a high-speed data acquisition card, the number of channels is 2, the sampling rate is 10GS/s, and the bandwidth is 10 GHz. The sensing optical fiber 3 is a refractive index graded multi-mode optical fiber.
The invention also provides a detection method of the distributed optical fiber Raman sensing system facing the smart grid, which mainly comprises the following steps:
the method comprises the following steps: a distributed optical fiber sensing system as shown in fig. 1 was constructed.
As shown in fig. 1, the output of the pulse laser 1 is connected to a first port a of the wavelength division multiplexer, the second port b of the wavelength division multiplexer 2 is connected with the first port a of the sensing optical fiber 3, the sensing optical fiber 3 is 5m away from the second port b of the wavelength division multiplexer 2, a part of the sensing optical fiber 3 with the length of 1m is placed in the thermostatic bath 10, the third port c of the wavelength division multiplexer 2 is connected with the input end of the avalanche photodetector 4, the fourth port d of the wavelength division multiplexer 2 is connected with the input end of the avalanche photodetector 5, the output end of the avalanche photodetector 4 is connected with the input end of the amplifier 6, the output end of the avalanche photodetector 5 is connected with the input end of the amplifier 7, the output ends of the amplifier 6 and the amplifier 7 are connected with the input end of the high-speed data acquisition card 8, and the output end of the high-speed data acquisition card 8 is connected with the computer 9. And the computer 9 is used for demodulating according to the acquired Raman anti-Stokes signals to obtain the distributed temperature field information along the sensing optical fiber 3.
Step two: and (4) performing light intensity processing on the Raman light and the Raman anti-Stokes signal.
In conventional temperature demodulation, the light intensities of the raman stokes light and the anti-stokes scattering signal excited at the position of the sensing fiber L are:
wherein Is(T, L) and Ia(T, L) are respectively the intensity of Raman Stokes scattered light and the intensity of Raman anti-Stokes scattered light amplified by an electrical amplifier in relation to temperature and position, where Ms、MaAmplification factor, K, of Raman Stokes scattered light and Raman anti-Stokes scattered light respectively by light amplification systems、KaScattering cross section coefficients, v, of Raman Stokes scattered light and Raman anti-Stokes scattered light, respectivelys、νaOptical frequencies of Raman Stokes scattered light and Raman anti-Stokes scattered light, respectively, I0Is the intensity of incident light, alpha0、αs、αaThe attenuation coefficients of incident light, raman stokes light and raman anti-stokes light in the optical fiber, respectively, L is the position of the optical fiber and T is the temperature at the L position. h is Planck constant. Δ ν is the raman shift, equal to 13.2THz, k is the boltzmann constant.
The distributed optical fiber Raman sensing system utilizes a pulse time flight method to carry out space positioning, and the influence of pulse width on the system positioning is usually ignored in the traditional theoretical analysis. Because the pulse has width, the information acquired by the high-speed data acquisition card at any time is not the light intensity information of one point at the position of the optical fiber L, but the superposition of Raman anti-Stokes light intensity information of the whole laser pulse in the optical fiber sensing distance equal to half pulse time scale. For example, when the pulse width of the detection signal is 10ns, the high-speed data acquisition card is used for acquiring a pulse with the light intensity of the backward raman anti-stokes signal actually 10ns at the position corresponding to the optical fiber L, and the sensing distance of the optical fiber is equal to half of the pulse time scale, that is, the superposition in 5ns, the length of the corresponding sensing optical fiber is 1m, and the specific expression is as follows:
in the formula (I), the compound is shown in the specification,
the light intensity of the data acquisition card collected at the position of the sensing optical fiber L is accumulated, and when the pulse width is 10ns, the accumulation length is L-1-L]I.e. 5ns corresponds to a light propagation distance which is the sampling interval. Similarly, the light intensity of the backward raman stokes light signal is actually:
step three: and performing Raman Stokes and anti-Stokes signal processing in a calibration stage.
The pulse laser 1 emits laser pulses (1550nm) having a pulse width of 10ns, and the laser pulses are incident into the sensing fiber 3 via the wavelength division multiplexer 2. Backward raman scattering anti-stokes light (1450nm) generated in sensing light enters the first photoelectric detector 4 and the second photoelectric detector 5 through the wavelength division multiplexer 2 to convert optical signals into electric signals, the electric signals sequentially pass through the first amplifier 6, the second amplifier 7 and the high-speed data acquisition card 8 to complete amplification and analog-to-digital conversion, and finally enter the computer 9, so that the position and light intensity information of the raman stokes light and the anti-stokes light is obtained.
Setting the environmental temperature of the whole sensing optical fiber in the calibration stage asT0The light intensity of the backward raman anti-stokes scattered light of the sensing fiber 3 at the L position, which is acquired by the high-speed data acquisition card 8, can be expressed as:
the raman stokes light intensity can be expressed as:
since the sampling rate of the selected high-speed data acquisition card 8 is 10GS/s, the sampling period is 1% of the pulse width (corresponding to 1cm of the optical fiber length). Thus, 99% of the information collected for each discrete point's data value as represented in the previous data point is information representing the same location on the fiber. Since the temperature in the constant temperature bath is constant, the energy loss of the pulse laser in a short distance (1m) is ignored, and then it is considered that the light intensity of the backward raman stokes light and the anti-stokes scattered light at each position in the constant temperature bath is kept constant, and can be expressed as:
wherein, Tc0The constant temperature is the temperature of the constant temperature bath, and d is the length of the corresponding optical fiber accumulated by the light intensity collected at the sensing optical fiber L.
Since 99% of the information collected for each discrete point is information representing the same location on the fiber as the data represented in the previous data point. Therefore, the light intensity of the backward Raman anti-Stokes scattered light of the first measurement interval (the length is 1% of the sampling interval) of the sensing fiber outside the constant temperature bath can be expressed as:
Ial1(T0,L)＝Ia1'-Ia0'+0.01Ia0'； (9)
wherein, Ial1Indicating the intensity of the backscattered Raman anti-Stokes light obtained in the first interval, Ia0' indicates data in which all the information on the last measured temperature is contained in the thermostatic bath, wherein Ia0’＝100Ial0，Ia1' denotes the first Raman anti-Stokes light intensity data measured in the sensing fiber outside the thermostatic bath, and so on, Ian' denotes the nth raman anti-stokes light intensity data measured outside the oven. From this, the light intensity of the backward raman anti-stokes scattered light in the subsequent measurement interval is:
after 100 calculations, Ia101' and Ia100' the temperature information contained is not already information about the optical fiber located in the thermostatic bath, so from Ial101Initially, the corresponding processed information, i.e. I, should be subtractedac1. When the pulse width is X times the length of the interval, expressions (9) and (10) can be written as:
equation (11) can be finally expressed as:
the value range of X depends on the performance of the signal acquisition equipment and the noise suppression capability of the system. I isalnRepresenting the intensity of the back-Raman anti-Stokes scattered light obtained in the nth measurement interval during the calibration phase, wherein Ian' and Ia(n-1)' n-th sum of optical fibers outside the thermostat obtained in the calibration stageBackward Raman anti-Stokes scattered light intensity data of the (n-1) th sampling interval, Ial(n-X)Indicating the light intensity of the backward Raman anti-Stokes scattered light of the n-X measuring interval outside the constant temperature bath obtained in the calibration stage, wherein X is equal to the ratio of the pulse width to the length of the sampling interval, Ia0' data indicating the last sampling interval in the thermostatic bath obtained in the calibration phase, Ia0’＝X·Ial0. As can be seen from the above formula, the light intensity of the backward raman anti-stokes scattered light for each measurement interval can be derived by formula (12).
As before, the intensity of the backward raman stokes light for each measurement interval can be expressed as:
wherein, Isn' and Is(n-1)' indicating the intensity of the backward Raman Stokes scattered light in the n-th and n-1-th sampling intervals of the fiber outside the thermostat obtained in the calibration stage, respectively, Isl(n-X)Indicating the light intensity of backward Raman Stokes scattered light of the n-X measurement interval outside the constant temperature bath obtained in the calibration stage; i iss0' represents the intensity of the Stokes light of the last sampling interval in the thermostatic bath obtained in the calibration phase, wherein Is0’＝X·Isl0，Isl0And the light intensity of backward Raman Stokes light in a certain sampling interval measured in the constant temperature bath in the calibration stage is shown.
As shown in fig. 2, in a conventional raman system, a light time domain reflection technique is used, and light intensity information acquired at each moment is superposition of temperature signals corresponding to a section of length in an optical fiber (i.e. I in fig. 2)anOr Ia(n-1)) And therefore limited spatial resolution, the embodiment subtracts the repeated parts of the two data by increasing the sampling rate to finally obtain IalnThe range of information contained becomes smaller, IalnThe corresponding information range is the measurement interval of the application, IanThe corresponding information range is the sampling interval of the present application,therefore, the data among all the cells can be obtained by a difference-by-difference method, and the spatial resolution of the sensing system is improved. The same is true for stokes light.
Step four: raman Stokes signal and Raman anti-Stokes signal processing in measuring stage
The pulse laser 1 emits laser pulses with the pulse width of 10ns, the temperature and the position along the sensing optical fiber 3 are respectively represented by T and L, the high-speed data acquisition card 8 receives backward Raman anti-Stokes scattered light at each position of the sensing optical fiber 3, and the light intensity is represented as follows:
the high-speed data acquisition card 8 receives backward Raman Stokes scattered light at each position of the sensing fiber 3, and the light intensity is expressed as:
wherein Is(T, L) and Ia(T, L) are respectively the backward Raman Stokes scattered light intensity and the backward Raman anti-Stokes scattered light intensity which are amplified by an electrical amplifier and are related to the temperature and the position, wherein Ms、MaAmplification factor, K, of Raman Stokes scattered light and Raman anti-Stokes scattered light respectively by light amplification systems、KaScattering cross section coefficients, v, of Raman Stokes scattered light and Raman anti-Stokes scattered light, respectivelys、νaOptical frequencies of Raman Stokes scattered light and Raman anti-Stokes scattered light, respectively, I0Is the intensity of incident light, alpha0、αs、αaThe attenuation coefficients of incident light, Raman Stokes light and Raman anti-Stokes light in the optical fiber respectively, L is the position of the optical fiber, and T is the temperature of the L position. h is Planck constant. Δ ν is the raman shift, equal to 13.2THz, k is the boltzmann constant.
The temperature of the thermostatic bath is set to be T in the measuring stagecThe light intensity of the backward raman anti-stokes scattered light at each position in the thermostatic bath is equal, and can be expressed as:
the intensity of the backward Raman Stokes scattered light at each position in the constant temperature bath is equal, and can be expressed as:
wherein, TcThe constant temperature is the temperature of the constant temperature bath, and d is the length of the corresponding optical fiber accumulated by the light intensity collected at the sensing optical fiber L. As with the calibration stage processing method, the light intensity of the backward raman anti-stokes scattered light in the first measurement interval (1% of the sampling interval) in which the sensing fiber is located outside the thermostatic bath can be expressed as:
Iac1(T,L)＝Ia1-Ia0+0.01Ia0； (18)
in the scaling stage of step three, when the pulse width is X times the length of the interval, the expression can be written as:
where equation (19) can be written finally:
the value range of X depends on the performance of the signal acquisition equipment and the noise suppression capability of the system. Wherein, Iac1Indicating the intensity of the backscattered Raman anti-Stokes light obtained in the first interval, Ia1Representing the first measured data relating to the fiber outside the oven; i isanAnd Ia(n-1)Respectively showing the backward Raman anti-Stokes scattered light intensity data of the nth and the n-1 th sampling intervals of the optical fiber outside the constant temperature bath obtained in the measuring stage, Iac(n-X)Indicating the intensity of the backward Raman anti-Stokes scattered light obtained in the measurement phase in the n-X measurement interval outside the thermostatic bath, Ia0Data representing the last sampling interval in the thermostatic bath obtained during the measurement phase, Ia0＝X·Iac0(ii) a Wherein, IacnIndicating the light intensity of the backward raman anti-stokes scattered light obtained in the nth interval. From the above formula, the light intensity of the backward raman anti-stokes scattered light in the measurement region of each sensing fiber can be derived by formula (20).
As before, the stokes light scattering intensity can be expressed as:
Isnand Is(n-1)Respectively showing the light intensity, I, of backward Raman Stokes light of the n-1 th sampling interval and the n-th sampling interval of the optical fiber outside the thermostatic bath obtained in the measuring stagesc(n-X)Indicating the intensity of backward Raman Stokes light in the n-X measurement interval outside the thermostatic bath obtained in the measurement stage, Is0Light intensity, I, of Stokes light representing a sampling interval in a thermostatic bath obtained during a measurement phases0＝X·Isc0。
Step five: demodulation temperature
In the measuring stage, the calculation formulas of the Raman anti-Stokes light intensity and the Stokes light intensity of each measuring interval along the sensing optical fiber 3 are respectively as follows:
in addition, the calculation formulas of the raman anti-stokes light intensity and the raman stokes light in each measurement interval along the sensing fiber 3 in the calibration stage are as follows:
the vertical type (7), (8), (16), (17), (22), (23), (24) and (25) can obtain:
obtaining by solution:
t in the formula (27) is the temperature distribution along the optical fiber, TcFor measuring the temperature value, T, of the thermostatic bath 100For calibrating the temperature value, T, of the sensing fiber in the phasec0Is the temperature value of the thermostatic bath 10 at the time of calibration. I isal0Indicating the intensity of the backward Raman anti-Stokes scattered light, I, of the respective measurement interval in the thermostatic bath obtained in the calibration phasealnIndicating the intensity of the backward Raman anti-Stokes scattered light of the nth measurement interval of the sensing fiber outside the thermostatic bath obtained in the calibration stageac0Indicating the intensity of the backward Raman anti-Stokes scattered light of each measurement interval in the thermostatic bath obtained during the measurement phase, IacnThe optical intensity of backward Raman anti-Stokes scattered light obtained in the nth measurement interval of the sensing optical fiber outside the constant temperature bath in the measurement stage is represented; i issl0Indicating the intensity of the backward Raman Stokes scattered light of each measurement interval in the thermostatic bath obtained in the calibration phase, IslnBackward Raman Stokes scattering of nth measurement interval of sensing fiber outside thermostatic bath obtained in calibration stageIntensity of the emitted light, Isc0Indicating the intensity of the backward Raman Stokes scattered light of each measurement interval in the thermostatic bath obtained in the measurement phase, IscnAnd the light intensity of backward Raman Stokes scattered light obtained in the nth measurement interval of the sensing optical fiber outside the constant temperature bath in the measurement stage is shown, and n is a positive integer greater than zero.
In summary, the invention provides a distributed optical fiber raman sensing system and method facing to pipe network leakage, which improves the spatial resolution of the system by improving the sampling rate of the system and performing reconstruction and layered analysis on the original signals superposed together, and can optimize the spatial resolution of the system to 1 cm. Moreover, the front end of the sensing optical fiber is provided with the constant temperature groove, random noise in equipment such as light source output and APD (avalanche photo diode) can be eliminated, and the sensing signals are demodulated through two paths of light, so that the system has higher temperature measurement precision and is more sensitive to small changes, and therefore, the invention not only improves the resolution ratio of the system, but also improves the measurement precision.
Finally, it should be noted that: the above embodiments are only used to illustrate the technical solution of the present invention, and not to limit the same; while the invention has been described in detail and with reference to the foregoing embodiments, it will be understood by those skilled in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some or all of the technical features may be equivalently replaced; and the modifications or the substitutions do not make the essence of the corresponding technical solutions depart from the scope of the technical solutions of the embodiments of the present invention.
Claims (8)
1. The distributed optical fiber sensing system facing the smart power grid is characterized by comprising a pulse laser (1), a wavelength division multiplexer (2), a sensing optical fiber (3), a first photoelectric detector (4), a second photoelectric detector (5) and a data acquisition system, wherein pulse laser output by the pulse laser (1) is incident to the sensing optical fiber (3) after passing through the wavelength division multiplexer (2), Stokes light and anti-Stokes light reflected in the sensing optical fiber (3) are detected by the first photoelectric detector (4) and the second photoelectric detector (5) after passing through the wavelength division multiplexer (2), one part of the sensing optical fiber (3) is arranged in a constant temperature tank (10), and the constant temperature tank (10) is used for carrying out constant temperature control on the sensing optical fiber (3) positioned in the constant temperature tank; stokes signals and anti-Stokes signals detected by the first photoelectric detector (4) and the second photoelectric detector are collected and demodulated by a data collection system to obtain distributed temperature field information along the sensing optical fiber (3); the temperature demodulation formula is as follows:
wherein T represents the temperature of the nth measuring interval of the sensing optical fiber outside the thermostatic bath,kis the boltzmann constant, and is,△νin order to be the raman shift frequency,his the constant of the Planck, and is,T cfor measuring the set temperature, T, of the thermostatic bath during the phasec0For calibrating the set temperature, T, of the thermostatic bath0Sensing the ambient temperature of the fiber for calibration stage, Ial0Indicating the intensity of the backward Raman anti-Stokes scattered light, I, of the respective measurement interval in the thermostatic bath obtained in the calibration phasealnIndicating the intensity of the backward Raman anti-Stokes scattered light of the nth measurement interval of the sensing fiber outside the thermostatic bath obtained in the calibration stageac0Indicating the intensity of the backward Raman anti-Stokes scattered light of each measurement interval in the thermostatic bath obtained during the measurement phase, IacnThe optical intensity of backward Raman anti-Stokes scattered light obtained in the nth measurement interval of the sensing optical fiber outside the constant temperature bath in the measurement stage is represented; i issl0Indicating the intensity of the backward Raman Stokes scattered light of each measurement interval in the thermostatic bath obtained in the calibration phase, IslnIndicating the intensity of the backward Raman Stokes scattered light of the nth measuring interval of the sensing fiber outside the thermostatic bath obtained in the calibration stagesc0Light intensity of backward Raman Stokes scattered light representing each measurement interval in the thermostatic bath obtained in the measurement stage, IscnIndicating the light intensity of backward Raman Stokes scattered light obtained in the nth measuring interval of the sensing fiber outside the thermostatic bath in the measuring stage,n is a positive integer greater than zero.
2. A distributed fibre optic sensing system towards a smart grid according to claim 1, characterized in that the data acquisition system comprises a data acquisition card (8) and a calculation unit (9).
3. The distributed optical fiber sensing system facing the smart grid according to claim 2, further comprising a first amplifier (6) and a second amplifier (7), wherein output signals of the first photodetector (4) and the second photodetector (5) are collected by the data collection card (6) after passing through the amplifier (5).
4. The distributed optical fiber sensing system facing the smart grid according to claim 2, wherein the sampling rate of the data acquisition card (8) is 10GS/s, and the bandwidth is 10 GHz.
5. The distributed optical fiber sensing system facing the smart grid according to claim 1, wherein the pulse laser (1) has a wavelength of 1550nm, a pulse width of 10ns, and a repetition rate of 6 KHz; the bandwidths of the first photoelectric detector (4) and the second photoelectric detector (5) are 100MHz, and the spectral response range is 900-1700 nm; the sensing optical fiber (3) is a refractive index graded multi-mode optical fiber.
6. The distributed optical fiber sensing system for the smart grid according to claim 1, wherein Ialn、Isln、Iacn、IscnThe calculation formula of (2) is as follows:
wherein X is equal to the ratio of the pulse width to the length of the sampling interval;I an ' andI a n-1（）' indicating the intensity of the backward Raman anti-Stokes scattered light in the nth and the n-1 th sampling intervals of the fiber outside the thermostat obtained in the calibration stage, respectively, Ial（n- X）Indicating the light intensity of the backward Raman anti-Stokes scattered light of the n-X measuring interval outside the constant temperature bath obtained in the calibration stage,I a0 ’representing the light intensity of the anti-stokes light of the last sampling interval in the constant temperature bath obtained in the calibration stage;
I sn ' andI s n-1（）' indicates the intensity of the backward Raman Stokes scattered light of the nth and the (n-1) th sampling intervals of the fiber outside the thermostatic bath obtained in the calibration stage respectively, Isl（n- X）Indicating the light intensity of backward Raman Stokes scattered light of the n-X measurement interval outside the constant temperature bath obtained in the calibration stage;I s0 ’the light intensity of Stokes light of a sampling interval in the constant temperature bath obtained in the calibration stage is represented;
I an andI a n-1（）respectively showing the light intensity, I, of backward Raman anti-Stokes light in the n-1 th and n-th sampling intervals of the optical fiber outside the thermostatic bath obtained in the measuring stageac（n-X）Indicating the backward Raman anti-Stokes light intensity of the n-X measuring interval outside the constant temperature bath obtained in the measuring stage,I a0a light intensity of anti-stokes light representing one sampling interval in the thermostatic bath obtained in the measurement phase;
I sn andI s n-1（）respectively showing the light intensity, I, of backward Raman Stokes light of the n-1 th sampling interval and the n-th sampling interval of the optical fiber outside the thermostatic bath obtained in the measuring stagesc（n-X）Indicating measurement phase acquisitionThe n-X measurement interval outside the constant temperature bath, the backward Raman Stokes light intensity,I s0representing the intensity of the stokes light of the last sampling interval in the thermostatic bath obtained during the measurement phase.
7. A distributed optical fiber sensing detection method for a smart grid is characterized by being realized by the distributed optical fiber sensing system for the smart grid according to any one of claims 1 to 6, and comprising the following steps:
s1, calibration stage: the temperature of the constant temperature bath is set toT c0 The ambient temperature of the sensing fiber is set to T0Setting the sampling period of the data acquisition system to be 1/X of the width of a single pulse, and acquiring the light intensity of Raman anti-Stokes light and Stokes light reflected in the sensing optical fiber by using the data acquisition system, including the light intensity I of backward Raman anti-Stokes light in each sampling interval of the sensing optical fiber in the thermostatic batha0' and intensity of backward Raman Stokes light Is0' and the light intensity I of backward Raman anti-Stokes light obtained in each sampling interval of the sensing fiber outside the thermostatic bathan' and intensity of backward Raman Stokes light Isn’；
S2, measurement stage: the temperature of the constant temperature bath is set toT cSetting the same sampling period, and acquiring the light intensities of all Raman anti-Stokes lights and anti-Stokes lights in the sensing optical fiber by using a data acquisition system, including the light intensity I of the backward Raman anti-Stokes scattered light in each sampling interval of the sensing optical fiber in the thermostatic batha0And the intensity of the backscattered Raman Stokes light Is0And the light intensity I of backward Raman anti-Stokes light obtained in each sampling interval of the sensing optical fiber outside the constant temperature bathanAnd the intensity of backward Raman Stokes light Isn；
And S3, calculating and demodulating the data obtained by measurement in the steps S1 and S2 to obtain the distributed temperature field information along the sensing optical fiber (3).
8. The distributed optical fiber sensing detection method for the smart grid according to claim 7, wherein the value of X is 100.
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